The present disclosure relates, broadly, to the field of power generation used to produce electricity. More particularly, the disclosure relates to a modular, shop-assembled solar receiver. The receiver comprises an arrangement of heat transfer surfaces or facets, a molten salt heat transfer system structurally and fluidically interconnected thereto, and an integral support structure, among other components. Also disclosed is a power generation system using such a shop-assembled solar receiver.
Generally, a solar receiver is a component of a solar energy generation system whereby radiation from the sun (i.e. sunlight) is used as a heat source. The radiation and heat energy from the sun is transferred to a working fluid which is used to ultimately generate electricity through the use of turbines, etc. The receiver is usually a large unit permanently mounted on top of an elevated support tower that is strategically positioned in a field of heliostats, or mirrors, that collect rays of sunlight and reflect those rays back to target walls in the receiver. An efficient, compact solar receiver for such systems which uses molten salt or a similar heat transfer fluid and which is simple in design, modular, rugged in construction, and economical to manufacture, ship, and install would be desirable in the field of power generation.
Currently wind and solar photovoltaic power generators do not have economical energy storage capability. Without energy storage, fluctuations on the grid are inevitable due to changing winds, clouds, and darkness at night. As more solar electricity power generators are installed, fluctuations in the grid due to cloud passages and daily start up and shut down will be unacceptable to maintain demand. Ultimately, in order to control the grid, energy storage will be required. Molten salt solar plants with molten salt solar receivers may be helpful to meet this energy storage requirement, which allows for consistent and dispatchable electricity.
Unlike a steam/water solar power plant, a molten salt solar plant is able to efficiently store the collected solar energy as thermal energy, which allows the power generation to be decoupled from the energy collection. The power plant can then produce and dispatch electricity as needed, such as during cloud cover and at night, for some amount of time depending on the thermal storage system size.
A solar power plant that uses steam/water receivers and separately uses molten salt for thermal storage is possible, but less efficient. Additional heat exchangers would be required to transfer the thermal energy from the superheated steam, produced by the receivers, to heat the molten salt. The molten salt could then be stored, and when desired, electricity could be generated by pumping the hot salt to a different system of heat exchangers that transfer the thermal energy from the hot salt to water in order to produce steam to drive a conventional Rankine cycle turbine generator. Some problems with this system include the added cost of additional heat exchangers. Also, it would be difficult to design a steam/water receiver that is capable of producing hot enough steam to fully utilize the high temperature storage capability of the salt. Different heat transfer fluids (HTF) could be used for energy storage, such as oils used with parabolic trough technology, however these HTFs are limited to lower temperatures and are less efficient. Overall solar power plant efficiency would be lost through the additional heat exchangers and temperature limitations of different HTFs.
Along these lines, Gemasolar, a solar power plant located in Spain, utilizes a single, large field-erected molten salt solar receiver and was commissioned in Spring 2011. This project is designed to produce 17 megawatts electric (MWe) with 15 hours of energy storage.
A solar power plant project known as Solar Two was in operation from January 1998 to April 1999. Solar Two was intended to demonstrate the potential use of molten salt solar power tower technology on a commercial scale. FIG. 1 is a perspective drawing of the Solar Two receiver.
The solar receiver used in Solar Two was a single, field-erected receiver in a heliostat field. The receiver consisted of 24 panels in an external cylindrical arrangement surrounding the internal piping, instrumentation, and salt holding vessels (not visible). Each of the panels consisted of 32 thin walled tubes constructed of stainless steel and coated with black paint in order to absorb the maximum amount of incident solar energy from the heliostat field.
FIG. 2 is a schematic of flow paths of the Solar Two receiver. The first flow path is the bypass flow path. “Cold” molten salt could flow up riser 202 and into inlet vessel 210. Upon opening of the bypass valve 208, the molten salt would flow through bypass line 206 directly into downcomer 204, bypassing the panels and the outlet vessel 220. The second flow path flows through the receiver panels to heat up the molten salt. Cold molten salt flowed from inlet vessel 210 through pipe 230 into and through the panels, then flowed into outlet vessel 220. Drain valves 240, ring header 242, and vent valves 244 are also illustrated.
It would be desirable to provide a compact solar receiver that uses molten salt or a similar heat transfer fluid and which is simple in design, modular, and economical.